The present invention is concerned with slicing machines, and more particularly is directed to a novel method and apparatus for automatically trimming a certain number of slices from the leading edge of a food product.
In the slicing of food products, for example the slicing of pork bellies into bacon strips, the slicing operation is carried out in cyclic fashion wherein during each cycle a predetermined number of slices, forming a group known as a draft, are removed from the product. After one draft is sliced, the slicing operation is momentarily interrupted while this draft is carried away from the slicing blade, for example by a conveyor belt, and then the slicing of the next draft begins so that there is a discernible space between adjacent drafts. These drafts are individually classified according to the quality of the meat slices therein and sold at prices relating to their respective classification.
In certain types of food products such as pork bellies, the leading edge of the product that is presented to the slicing blade by a feeding mechanism is not squarely cut. For example, the front edge of the product might be rounded or somewhat uneven. Consequently, the first few slices that are taken from the leading edge of the product have an irregular shape and a width that is much less than that of slices taken from the center of the product, for example.
If the first few slices taken from the pork belly are included in the first draft of bacon slices, this draft will necessarily have to be downgraded, i.e., it will be less than premium quality, because of these few slices, even though the majority of the slices might be of top quality. These downgraded slices are sold at a lower price or used to make other products, such as sausage for example. On the average, about 1/2 pound of top quality slices in a 12 pound pork belly would be unnecessarily downgraded when the first few slices are included in a draft. Accordingly, it is a common practice in the food processing industry to trim the first 4-6 slices off the leading edge of the pork belly before beginning on the first draft. With this approach, the first slice in the first draft will be a top quality slice and therefore more of the bacon from the pork belly can be sold as higher grade bacon.
In the past, the trimming of the first few slices from the pork belly was carried out manually. Typically, an operator stationed adjacent the slicing blade of the slicing machine would observe the pork belly as it was being sliced. When the operator saw that the irregular slices had been removed from the pork belly and that full slices were about to be cut, he or she would actuate a trim button which would cause the slicing operation to be temporarily interrupted. The effect of this interruption was to allow the irregular slices that had just been trimmed from the leading edge of the pork belly to be removed from the location of the slicing blade so that they would be separated from the first draft which was to be cut after the interruption had ceased.
A limitation associated with the manual trimming approach is the fact that a slicing machine operates at a much faster rate than that at which an observer can respond. For example, a modern slicing machine, while operating at full speed, might slice a strip of bacon from the pork belly every forty milliseconds. The average human typically can not respond within such a short period of time, particularly if he or she is nearing the end of the work shift and is tired from doing the same job for 6-8 hours. Consequently, two or three good slices of bacon might be included with the irregular slices before the trim button is actuated. Conversely, if the operator tries to anticipate when the slicing of full slices will begin, actuation of the button too soon will result in a partial slice being included in the first draft, and hence that draft will be downgraded. Thus, while the manual control over the trimming of the leading slices from the pork belly has resulted in some savings in the food processing industry, it has not maximized the quantity of bacon slices from a pork belly that can be sold as top quality bacon.
A slicing machine in which the first few slices are automatically removed from the leading edge of a pork belly, rather than manually, is disclosed in U.S. Pat. No. 3,131,739. In this automatic control system, a mechanical probe is placed in the path of the pork bellies as they are being fed to the slicing blade. The probe is displaced by the leading edge of a belly as it reaches a predetermined point. This point is related to the number of slices that are to be included in each draft, and the number of slices that are to be removed from the leading edge. For example, if each draft is to include 18 slices, and the first 6 slices are to be removed from the leading edge, the probe is placed at a point where it would be actuated when the leading edge of the pork belly is a distance from the blade equal to the thickness of 12 (i.e. 18 minus 6) slices. When the probe is actuated by the leading edge, it energizes a counting mechanism which controls the operation of the slicer in accordance with the number of slices to be included in each draft. Thus, when the leading edge of the pork belly is a distance equal to the thickness of 12 slices from the slicing blade, the counting mechanism would begin to count the number of rotations of the slicing blade as the pork belly continues to advance. For the first 12 rotations, no slicing would be carried out since the pork belly has not yet reached the blade. However, on the 13th through the 18th rotation, the first 6 slices would be removed from the leading edge of the pork belly. Once the counter determines that 18 rotations of the blade have taken place, the slicing operating is momentarily interrupted to provide the usual spacing between drafts. In this case, however, the spacing which is provided is between the first few irregular slices and the first draft which is about to be sliced.
While the automatic control mechanism disclosed in the '739 patent offers advantages over the manual trimming procedure, it is also limited in its practical applications. More particularly, the '739 patent is concerned with reciprocating type slicers, in which the pork bellies are fed to the blade one at a time. Typically, these types of slicers would employ a feed mechanism having a ram that would push one belly forward into the slicer. After the slicing of the belly was completed, the ram would be retracted and a new belly would be placed in position to be fed to the blade by the ram. The mechanical probe approach is really only suited for use with reciprocating type slicers, because in these machines the probe has an opportunity to drop between adjacent bellies. If the bellies are lined up in end-to-end abutment on a conveyor that continuously feeds them to the slicing blade, as is typically done in more modern slicing machines, the mechanical probe may remain in its displaced position and never detect the leading edge of the second and subsequent pork bellies. Instead, it could merely ride on the tops of the bellies from one to the next. Thus, it would not function to trim the first few slices from the leading edge of the following pork bellies.
Typically, when the pork bellies are in end-to-end abutment in a continuous feed slicer, small gaps will appear at various points along the interface of two adjacent pork bellies because their abutting ends are not squarely cut. These gaps might provide possible sources for actuation of a probe. However, the location of these gaps will vary from interface to interface because of the irregularity of each end. Thus, a single probe would not be successful in detecting a gap at each interface. To ensure adequate detection, a number of probes would have to be located across the width of the belly. Such an approach becomes quite complex and cumbersome.
In any event, even if a probe is in alignment with the gap between bellies in a continuous feed slicer, the mechanical sensing technique is not capable of responding within the short times required by modern operations. For example, the gap at the interface between bellies might typically be equal to the width of 2-3 slices. If a slice is removed every 40 msec, the probe only has 80-120 msec to fall into the gap and then be displaced again. On a practical level, this time period is simply too short for a mechanical probe to detect a gap with a reasonable degree of reliability.
Furthermore, even if the pork bellies are spaced along the conveyor belt in a continuous feed slicer so that the mechanical probe has an adequate chance to drop between adjacent bellies, they must be spaced a distance that is greater than the difference between a number of slices in a normal draft and the number of slices to be trimmed from the leading edge, i.e., more than 12 slices in the preceding example. If this spacing is not provided, the counter might be actuated by the leading edge of the second pork belly before it has finished counting the number of slices in the final draft of the preceding pork belly. For example, if the counter is re-set by the mechanical probe after it has only counted 15 slices on the preceding draft because the following belly is too close, it will cause the slicing operation to continue for another 18 slices. This action will result in more than the required number of slices being included in the last draft of the preceding pork belly.
Thus, if the pork bellies are spaced too close to one another, the mechanical probe approach can result in significant waste from too many slices being included in a draft. Conversely, if the spacing between adjacent pork bellies is large enough for the probe to operate properly, significant delays will be encountered in the slicing operation due to the "dead time" between the slicing of pork bellies.